Sahih Muslim Book - 39, Hadith - 5846

وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللهِ ، عَنْ سُهَيْلٍ ، عَنْ أَبِيهِ ، عَنْ أَبِي هُرَيْرَةَ ، قَالَ : قَالَ رَسُولُ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: مَنْ قَتَلَ وَزَغَةً فِي أَوَّلِ ضَرْبَةٍ فَلَهُ كَذَا وَكَذَا حَسَنَةً ، وَمَنْ قَتَلَهَا فِي الضَّرْبَةِ الثَّانِيَةِ فَلَهُ كَذَا وَكَذَا حَسَنَةً ، لِدُونِ الأُولَى ، وَإِنْ قَتَلَهَا فِي الضَّرْبَةِ الثَّالِثَةِ فَلَهُ كَذَا وَكَذَا حَسَنَةً ، لِدُونِ الثَّانِيَةِ.

It was narrated that Abu Hurairah said: “The Messenger of Allah (s.a.w) said: ‘Whoever kills a geckos with the first blow will have such and such of Hasanah (good merit). Whoever kills it with the second blow will have such and such of Hasanah, less than the first. Whoever kills it with the third blow will have such-and-such of Hasanah, less than the second.”’